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| United States Patent |
5,516,615
|
|
Tyagi
, et al.
|
May 14, 1996
|
Stabilized carriers with .beta. phase poly(vinylidenefluoride)
Abstract
A method for converting .alpha.-phase poly(vinylidene fluoride) to
.beta.-phase poly(vinylidene fluoride), for preparing electrostatographic
carrier and, electrostatographic developer and carrier. In the method for
preparing electrostatographic carrier, uncoated electrostatographic
carrier particles are coated with .alpha.-phase poly(vinylidene fluoride)
to provide .alpha.-phase poly(vinylidene fluoride) coated carrier
particles. A measurable portion of the .alpha.-phase poly(vinylidene
fluoride) is then converted to .beta.-phase poly(vinylidene fluoride) by
subjecting the .alpha.-phase poly(vinylidene fluoride) to a series of
viscoelastic collisions having a total energy of from about
5.times.10.sup.4 to about 5.times.10.sup.5 Joules/kilogram of
poly(vinylidene fluoride).
| Inventors:
|
Tyagi; Dinesh (Fairport, NY);
Anderson; James H. (Rochester, NY);
DeMeyer; Dennis E. (Rochester, NY)
|
| Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
| Appl. No.:
|
381246 |
| Filed:
|
January 31, 1995 |
| Current U.S. Class: |
430/111.33; 430/111.35 |
| Intern'l Class: |
G03G 009/107; G03G 009/113 |
| Field of Search: |
430/106.6,108
|
References Cited
U.S. Patent Documents
| Re31072 | Nov., 1982 | Jadwin et al. | 430/99.
|
| 2229513 | Jan., 1941 | Lustig.
| |
| 3850663 | Nov., 1974 | Hagenbach | 430/108.
|
| 3893935 | Jul., 1975 | Jadwin et al. | 430/110.
|
| 3938992 | Feb., 1976 | Jadwin et al. | 430/109.
|
| 3970571 | Jul., 1976 | Olson et al. | 427/212.
|
| 4042518 | Aug., 1977 | Jones | 252/62.
|
| 4076857 | Feb., 1978 | Kasper et al. | 118/651.
|
| 4079014 | Mar., 1978 | Burness et al. | 430/110.
|
| 4089472 | May., 1978 | Siegel et al. | 241/5.
|
| 4160644 | Jul., 1979 | Ryan.
| |
| 4323634 | Apr., 1982 | Jadwin | 430/110.
|
| 4394430 | Jul., 1983 | Jadwin et al. | 430/110.
|
| 4414152 | Nov., 1983 | Santilli et al. | 430/114.
|
| 4416965 | Nov., 1983 | Sandhu et al. | 430/109.
|
| 4478925 | Oct., 1984 | Miskinis | 430/137.
|
| 4517171 | May., 1985 | Jadwin et al. | 430/110.
|
| 4536060 | Oct., 1985 | Miskinis et al. | 430/108.
|
| 4666813 | May., 1987 | Sakashita | 430/110.
|
| 4684596 | Aug., 1987 | Bonser et al. | 430/110.
|
| 4714046 | Dec., 1987 | Steele et al. | 118/657.
|
| 4726994 | Feb., 1988 | Yoerger | 430/108.
|
| 4737435 | Apr., 1988 | Yoerger | 430/137.
|
| 4758491 | Jul., 1988 | Alexandrovich et al. | 430/110.
|
| 4833060 | May., 1989 | Nair et al. | 430/137.
|
| 4878089 | Oct., 1989 | Guslits et al. | 355/253.
|
| 5192637 | Mar., 1993 | Saito et al. | 430/109.
|
| Foreign Patent Documents |
| 1148785 | Jun., 1983 | CA | 430/108.
|
| 1420839 | Jan., 1976 | GB.
| |
| 1501065 | Feb., 1978 | GB.
| |
Other References
M. Kobayashi et al, Macromolecules, vol. 8 (1981), pp. 158-171.
W. M. Priest, Jr. et al, J. Appl. Phys., vol. 46 (1975), pp. 4136-4143.
M. A. Marcus, "Ferroelectric Polymers and Their Applications," paper
presented at the Fifth International Meeting on Ferroelectricity at
Pennsylvania State University, Aug. 1981.
|
Primary Examiner: Martin; Roland
Attorney, Agent or Firm: Hawley; J. Jeffrey
Claims
What is claimed is:
1. An electrostatographic carrier comprising: carrier cores having a
coating of poly(vinylidene fluoride), said polyvinylidene fluoride having
a surface exposed to the ambient environment, said surface being at least
50 mole percent .beta.-phase poly(vinylidene fluoride).
2. The carrier of claim 1 wherein said poly(vinylidene fluoride) has a
concentration relative to said carrier cores of from about 0.001
weight/weight percent to about 5 weight/weight percent.
3. The carrier of claim 1 wherein said carrier cores are metallic.
4. The carrier of claim 1 wherein said carrier cores are strontium
ferrites.
5. Electrophotographic developer comprising the carrier of claim 1 and
toner.
6. The developer of claim 5 wherein said toner further comprises
styrenic/acrylic copolymer.
7. The developer of claim 5 wherein said toner further comprises a positive
charge control agent.
Description
FIELD OF THE INVENTION
The invention relates to electrophotography and to poly(vinylidene
fluoride). The invention more particularly relates to methods for changing
.alpha.-phase poly(vinylidene fluoride) to .beta.-phase poly(vinylidene
fluoride) and to the modification of poly(vinylidene fluoride) coated
electrophotographic carriers and to products of the methods.
BACKGROUND OF THE INVENTION
In electrostatography, image charge patterns are formed on a support and
are developed by treatment with an electrostatographic developer
containing marking particles which are attracted to the charge patterns.
These particles are called toner particles or, collectively, toner. The
image charge pattern, also referred to as an electrostatic latent image,
is formed on an insulative surface of an electrostatographic element by
any of a variety of methods. For example, the electrostatic latent image
may be formed electrophotographically, by imagewise photo-induced
dissipation of the strength of portions of an electrostatic field of
uniform strength previously formed on the surface of an
electrophotographic element comprising a photoconductive layer and an
electrically conductive substrate. Alternatively, the electrostatic latent
image may be formed by direct electrical formation of an electrostatic
field pattern on a surface of a dielectric material.
One well-known type of electrostatographic developer comprises a dry
mixture of toner particles and carrier particles. Developers of this type
are commonly employed in cascade and magnetic brush electrostatographic
development processes. The toner particles and carrier particles differ
triboelectrically, such that during mixing to form the developer, the
toner particles acquire a charge of one polarity and the carrier particles
acquire a charge of the opposite polarity. The opposite charges cause the
toner particles to cling to the carrier particles. During development, the
electrostatic forces of the latent image, sometimes in combination with an
additional applied field, attract the toner particles. The toner particles
are pulled away from the carrier particles and become electrostatically
attached, in imagewise relation, to the latent image bearing surface. The
resultant toner image can then be fixed, by application of heat or other
known methods, depending upon the nature of the toner image and the
surface, or can be transferred to another surface and then fixed.
A number of requirements are implicit in such development schemes. Namely,
the electrostatic attraction between the toner and carrier particles must
be strong enough to keep the toner particles held to the surfaces of the
carrier particles while the developer is being transported to and brought
into contact with the latent image, but when that contact occurs, the
electrostatic attraction between the toner particles and the latent image
must be even stronger, so that the toner particles are thereby pulled away
from the carrier particles and deposited on the latent image-bearing
surface.
Carrier particles comprise a core usually coated with a polymer. Commonly
used polymers include: silicone resin; acrylic polymers, such as,
poly(methylmethacrylate); and vinyl polymers, such as polystyrene and
combinations of materials. Another commonly used coating material is
fluorohydrocarbon polymer, such as poly(vinylidene fluoride) or
poly(vinylidene fluoride-co-tetrafluoroethylene). See, for example, U.S.
Pat. Nos. 4,546,060; 4,478,925; 4,076,857; and 3,970,571. Such polymeric
fluorohydrocarbon carrier coatings can serve a number of known purposes.
One such purpose can be to aid the developer to meet the electrostatic
force requirements mentioned above by shifting the carrier particles to a
position in the triboelectric series different from that of the uncoated
carrier core material, in order to adjust the degree of triboelectric
charging of both the carrier and the toner particles. Another purpose can
be to reduce the frictional characteristics of the carrier particles in
order to improve developer flow properties. Still another purpose can be
to reduce the surface hardness of the carrier particles so that they are
less likely to break apart during use and less likely to abrade surfaces,
such as photoconductive element surfaces, that they contact during use.
Yet another purpose can be to reduce the tendency of toner material or
other developer additives to become undesirably permanently adhered to
carrier surfaces during developer use (often referred to as "scumming"). A
further purpose can be to alter the electrical resistance of the carrier
particles. All of these, and even more, purposes are well known in the art
for polymeric fluorohydrocarbon carrier coatings. What is desired is a
carrier coating that serves all of the above-noted purposes well, both
initially and throughout a long useful life involving many replenishments
of toner.
Additional problems are faced by carriers used in electrophotographic
equipment in which there is a great deal of developer mixing, sometimes
referred to as "exercising". Examples of such equipment is disclosed in
U.S. Pat. Nos. 4,878,089 and 4,714,046. In such uses, loss of carrier
charge with exercising or aging is one of the biggest problem encountered.
This drop in charge with life leads to many problems which include
unacceptable dusting, poor image quality and reduced reliability of the
equipment. Among various techniques practiced to address this shortcoming,
preconditioning of the developer is by far the most common. In
preconditioning, carrier is mixed with toner, exercised and stripped
before use in the electrophotographic copier or printer. This initial
"aging" or treatment of the developer outside the equipment is expensive
and labor intensive and only addresses the problem of initial charge
instability. The problem that is not addressed is carrier aging that
occurs when the developer is exercised extensively when a very low amount
of toner is being developed or placed on each copy.
Various methods have been used to improve the characteristics of
fluorocarbon coated carriers. For example, U.S. Pat. No. 4,737,435 to
Yoerger, disclosed a method of dehydrofluorinating a fluorohydrocarbon
carrier coating by contacting the coated carrier particles with a basic
solution. The resulting change in chemical structure had the effect of
repositioning the carrier triboelectrically. In another example, U.S. Pat.
No. 4,726,994 to Yoerger, a method is disclosed for dehydrofluorinating
and oxidizing a fluorohydrocarbon carrier coating by contacting the coated
carrier particles with a basic solution and with an oxidizing agent. The
resulting change in chemical structure also had the effect of
repositioning the carrier triboelectrically, and in addition, decreased
overcharging.
Polyvinylidene Fluoride (PVF.sub.2) is commonly used as a carrier coating,
because it has a position in a triboelectric series with a variety of
electrophotographic toners that helps insure that a positive charge is
imparted to the toner and a negative charge to the carrier surface.
PVF.sub.2 can exist in a non-polar .alpha.-phase, and polar .beta., and
.gamma. phases. PVF.sub.2 is normally applied to carrier cores by melt
coating at a temperature in the range of about 190.degree. C. to
260.degree. C. PVF.sub.2 solidifies from a melt as .alpha.-phase. Melt
coating is highly preferred over solvent coating for environmental
reasons. M. Kobayashi, K. Tashiro and H. Tadokoro, Macromolecules., Vol.
8, p. 158 (1975) teaches the preparation of .alpha.-phase PVF.sub.2 by
stretching melt-crystallized specimens or by rolling film speciments cast
from dimethylacetamide solution. W. M. Priest, Jr., and D. J. Luca., J.
Appl. Phys., Vol. 46, p. 4136 (1975) teaches the preparation of
.beta.-phase PVF.sub.2 by poling. W. W. Doll and J. B. Lando, J. Macromol.
Sci.-Phys., Vol. B2, p. 219 (1968) teaches the preparation of .beta.-phase
PVF.sub.2 by high pressure crystallization. M. A. Marcus, paper presented
at the Fifth International Meeting on Ferroelectricity at Pennsylvenia
Sate University, Aug. 17-21, (1981) teaches the preparation of
.beta.-phase PVF.sub.2 by plastic deformation under high pressure. Such
procedures are expensive and complex.
There is thus a continuing need for a carrier that has good
electrophotographic properties, both initially and throughout a long
useful life involving many replenishments of toner and for developer
incorporating that carrier. There is also a continuing need for a simple,
inexpensive method for converting .alpha.-PVF.sub.2 to .beta.-PVF .sub.2.
SUMMARY OF THE INVENTION
The invention, in its broader aspects, provides a method for converting
.alpha.-phase poly(vinylidene fluoride) to .beta.-phase poly(vinylidene
fluoride), for preparing electrostatographic carrier and,
electrostatographic developer and carrier. In the method for preparing
electrostatographic carrier, uncoated electrostatographic carrier
particles are coated with .alpha.-phase poly(vinylidene fluoride) to
provide .alpha.-phase poly(vinylidene fluoride) coated carrier particles.
A measurable portion of the .alpha.-phase poly(vinylidene fluoride) is
then converted to .beta.-phase poly(vinylidene fluoride) by subjecting the
.beta.-phase poly(vinylidene fluoride) to a series of viscoelastic
collisions having a total energy of from about 5.times.10.sup.4 to about
5.times.10.sup.5 Joules/kilogram of poly(vinylidene fluoride).
It is an advantageous effect of at least some of the embodiments of the
invention that there is provided a method for modifying
electrophotographic carrier to provide a carrier that has good
electrophotographic properties, both initially and throughout a long
useful life. There is also advantageously provided a method for simply and
inexpensively converting .alpha.-PVF.sub.2 to .beta.-PVF.sub.2.
BRIEF DESCRIPTION OF THE FIGURES
The above-mentioned and other features and objects of this invention and
the manner of attaining them will become more apparent and the invention
itself will be better understood by reference to the following description
of an embodiment of the invention taken in conjunction with the
accompanying figures wherein:
FIGS. 1-3 are diagrams of the results of Example 13.
FIG. 4 is a diagram of the results of Example 14.
DESCRIPTION OF PARTICULAR EMBODIMENTS
The method of the invention provide a simple, economic procedure for
converting .alpha.-phase poly(vinylidene fluoride) to .beta.-phase
PVF.sub.2. In a preferred embodiment of the invention, the process is
performed on PVF.sub.2 -coated carrier particles to yield the carrier of
the invention. A developer of the invention, incorporating a carrier of
the invention, provides an unexpected improvement in charge stability
under unreplenished aging.
In the method of the invention, energy is imparted to an .alpha.-phase
PVF.sub.2 surface by a series of viscoelastic collisions of the surface
and other objects. The result is a conversion of the impacted PVF.sub.2
surface from .alpha.-phase to .beta.-phase. The collisions have a total
energy of from about 5.times.10.sup.4 to about 5.times.10.sup.5
Joules/kilogram of PVF.sub.2. The energy is applied to the PVF.sub.2 at a
rate of from about 5 to about 500 Watts/kilogram of PVF.sub.2.
The conversion of .alpha.-phase PVF.sub.2 to .beta.-phase can be detected
by a variety of techniques. For example, techniques suitable for use on a
PVF.sub.2 coated particulate include x-ray diffraction at a suitable
glancing angle and Fourier Transform Infrared Spectroscopy.
The PVF.sub.2 surface can be a coating on a particulate material, or can be
the coating on a panel or component made of another material, or can be
the surface layer of a PVF.sub.2 structural component.
The PVF.sub.2 coating can be uniform, or discontinuous. The PVF.sub.2
coating can also consist of crystalline PVF.sub.2 regions within a coating
of non-uniform composition. The remainder such a non-uniform coating can
be selected from a wide variety of crystalline or amorphous polymers, as
long as PVF.sub.2 rich regions are present. These PVF.sub.2 rich regions
may or may not consist of discrete domains. The additional polymer should
not deleteriously interfere with the intended characteristics of a
resulting product. For example, a low T.sub.g polymer could cause
unacceptable clumping of a coated particulate. Examples of suitable
coatings include: poly(methylmethacrylate) (PMMA), poly (styrene),
poly(siloxanes), silsesquioxanes, and poly(tetrafluroethelyne).
The manner in which the energy is supplied to the PVF.sub.2 surface, the
nature of the viscoelastic collisions, depends upon the physical
configuration of the PVF.sub.2 surface. For example, a large component
coated with PVF.sub.2 can be impacted with a high velocity flow of
particulate, or beads, or the like. This is generally comparable to a
variety of well-known procedures, for example, shot-peening; and details
of suitable techniques are well-known to those of skill in the art of
surface treatment.
With a coated particulate, collisional energy can be supplied by impacting
particles against each other. A variety of pulverizing and mixing
apparatus, designed to subject particulate materials to high shear, are
suitable for this purpose. Examples of such equipment are: Processall
mixer (manufactured by Processall Corp. Cincinnati, OH.), high shear
blender, fluid energy mill, ball mill. The magnetic particles could also
be impacted in a clean developer station removed from a Kodak 1575
Copier-Duplicator (manufactured by Eastman Kodak Company, Rochester, N.Y.)
or the equivalent.
In a preferred embodiment, the method of the invention is performed on
carrier cores coated with PVF.sub.2. The term "coated" should not be
understood to suggest or imply that the surface of the carrier cores is
necessarily completely covered with a uniform layer of PVF.sub.2. The
PVF.sub.2 may be coated over the bare cores on a very non-uniform basis
such that the PVF.sub.2 "coating" is seen as separated dark spots in
electron micrographs of carrier core particles.
In the method of the invention, the coated carrier particles are placed in
a high shear pulverizing device and the particles are impacted against
each other until at least 50 percent of the PVF.sub.2 surface has been
converted from .alpha.-phase to .beta.-phase. The 50 percent figure here
refers to a mole percent of the surface as measured by glancing angle
x-ray diffraction or the equivalent. It is expected that subsurface
portions of PVF.sub.2 will have a lesser percentage of .alpha. to .beta.
conversion. Carrier cores often have extensive surface convolutions. Those
convolutions are less accessible to PVF.sub.2 coating, .alpha. to .beta.
conversion, and surface analysis than non-convoluted portions of the
carrier and as a result can be ignored in considerations of PVF.sub.2
coating and conversion.
The method of the invention cannot be performed if necessary collisional
energy is absorbed by some material other than the .alpha.-phase
poly(vinylidene fluoride). For example, the .alpha.-PVF.sub.2 coating on
carrier particles, will not convert to .beta.-PVF.sub.2 if the carrier
particles are mixed with toner and then impacted together.
The method of the invention can be performed on carrier particles having
PVF.sub.2 as their only surface coating or having a coating applied as a
mixture of PVF.sub.2 and another polymer. If carrier particles can have
coats applied as multiple "layers", that is, applied in a multiple step
process; however, the PVF.sub.2 must remain subject to the energetic
collisions required by the method of the invention.
The carrier particles, also referred to as "carrier cores", can be
conductive, non-conductive, magnetic, or non-magnetic. Carrier particles
can be glass beads; crystals of inorganic salts such as aluminum potassium
chloride, ammonium chloride, or sodium nitrate; granules of zirconia,
silicon, or silica; particles of hard resin such as poly(methyl
methacrylate); or particles of elemental metal or alloy or oxide such as
iron, steel, nickel, carborundum, cobalt, oxidized iron and mixtures of
such materials. Examples of carrier cores are disclosed in U.S. Pat. Nos.
3,850,663 and 3,970,571. Especially useful in magnetic brush development
procedures are iron particles such as porous iron particles having
oxidized surfaces, steel particles, and other "hard" and "soft"
ferromagnetic materials such as gamma ferric oxides or ferrites of barium,
strontium, lead, magnesium, or aluminum. Such carriers are disclosed in
U.S. Pat. Nos. 4,042,518; 4,478,925; and 4,546,060. Currently preferred
are strontium ferrite carrier particles.
In currently preferred embodiments of the invention, the PVF.sub.2 is
coated over strontium ferrite carrier particles on an about 0.001 percent
to about 5 percent weight/weight basis. Coating percentages outside this
range may be utilized, however, concentrations of coating which would
cover an excessive portion of the surface of the carrier particles may
render electrophotographic properties of the resulting carrier unaccept. A
suitable coating percentage can be determined by simple experimentation.
If it is desirable to provide uniform coatings for batches of carrier
having different particle sizes, then the coating concentration should be
adjusted to provide a uniform weight of PVF.sub.2 per unit surface area of
carrier. A convenient coating concentration is a 2.0 percent weight/weight
basis when using about 25 microns volume average particle size. (The term
"particle size" used herein, or the term "size", or "sized" as employed
herein in reference to the term "particles", means the median volume
weighted diameter as measured by conventional diameter measuring devices,
such as a Coulter Multisizer, sold by Coulter, Inc of Hialeah, Fla. Median
volume weighted diameter is the diameter of an equivalent weight spherical
particle which represents the median for a sample.)
In preparing the developer of the invention, carrier particles prepared by
the method of the invention can be mixed with other carrier particles, for
example, PMMA coated carrier particles.
Carrier of the invention can be used in combination with a wide variety of
toners known in the art to be useful in combination with PVF2-coated
carrier particles and with any of the sizes and size ratios known to be
useful for such particles, to serve as dry electrostatographic developers
in any of the well known dry electroscopic development schemes, for
example, cascaded development or magnetic brush development.
In a particular embodiment, the developer of the invention contains from
about 1 to about 20 percent by weight of toner and from about 80 to about
99 percent by weight of carrier of the invention. Usually, carrier
particles are larger than toner particles. Conventional carrier particles
have a particle size of from about 5 to about 1200 micrometers and are
generally from 20 to 200 micrometers. Typically, and illustratively, the
toner particles have an average diameter between about 2.0 micrometers and
about 100 micrometers, and desirably have an average diameter in the range
of from about 5.0 micrometers and 30 micrometers for currently used
electrostatographic processes.
It is a characteristic of the developer of a preferred embodiment of the
invention that the charge development is uniform, that is, that
substantially all of the individual toner particles exhibit a
triboelectric charge of the same sign with respect to a given carrier.
Toner in a preferred embodiment of the invention achieves and maintains a
positive charge. Toner throw-off is minimimal. The term "toner throw-off"
refers to the amount of toner powder thrown out of a developer mix as it
is mechanically agitated, for example, within a development apparatus.
Throw-off can cause unwanted background development and general
contamination problems.
The properties of the thermoplastic polymers employed as the toner matrix
phase in the present invention can vary widely. Typically, and preferably,
amorphous toner polymers having a glass transition temperature in the
range of about 50.degree. C. to about 120.degree. C. or blends of
substantially amorphous polymers with substantially crystalline polymers
having a melting temperature in the range of about 65.degree. C. to about
200.degree. C. are utilized in the present invention. Preferably, such
polymers have a number average molecular weight in the range of about 1000
to about 500,000. The weight average of molecular weight can vary, but
preferably is in the range of about 2.times.10.sup.3 to about
1.times.10.sup.6 . Preferably, the thermoplastic polymers used in the
practice of this invention are substantially amorphous. However, as
indicated above, mixtures of polymers can be employed, if desired, such as
mixtures of substantially amorphous polymers with substantially
crystalline polymers.
Polymers useful as binders in the developer of the invention include
styrenic/acrylic copolymers. In general, preferred styrenic/acrylic
copolymers have a glass transition temperature in the range of about
50.degree. C. to about 100.degree. C. In a particular embodiment of the
invention, the resin is a copolymer of styrene and butyl acrylate,
crosslinked with divinyl benzene; produced in a suspension or emulsion
polymerization process. An initiator and, optional, a chain transfer agent
are used in the synthesis. The ratio of styrene to butyl acrylate is in
the range of from 90:10 to 60:40 and the divinyl benzene is used at a
level of 0.1 to 1.0 weight percent. A specific example of a toner binder
useful in the invention is disclosed in U.S. Pat. No. 3,938,992.
The toner can include charge control agent in an amount effective to
modify, and preferrably, improve the properties of the toner. It is
preferred that a charge control agent improve the charging characteristics
of a toner, so the toner quickly charges to a desired value and then
maintains about the same level of charge over a relatively extended time
period. In a currently preferred embodiment of the invention, a positive
charge control agent is used. Examples of charge control agents useful in
developers of the invention are disclosed in U.S. Pat. Nos. 3,893935;
4,079,014; and 4,323,634 and British Pat. Nos. 1,501,065; and 1,420,839.
Charge control agents are employed in small quantities such as, from about
0.1 to about 3 weight percent, or typically from about 0.2 to about 1.5
weight percent, all relative to the weight of the toner. Some examples of
charge control agents are quaternary ammonium salts that have long
hydrocarbon groups, such as: stearyl dimethyl benzyl ammonium chloride,
lauramidopropyl trimethyl ammonium methylsulfate and p-nitrobenzyl
dimethyloctadecyl ammonium chloride.
A variable component of the toner is colorant: a pigment or dye. Suitable
dyes and pigments are disclosed, for example, in U.S. Pat. No. Re. 31,072
and in U.S. Pat. Nos. 4,160,644; 4,416,965; 4,414,152; and 2,229,513. One
particularly useful colorant for toners to be used in black and white
electrostatographic copying machines and printers is carbon black.
Colorants are generally employed in the range of from about 1 to about 30
weight percent on a total toner powder weight basis, and preferably in the
range of about 2 to about 15 weight percent.
The toner can also contain other additives of the type used in previous
toners, including leveling agents, surfactants, stabilizers, and the like.
The total quantity of such additives can vary. A present preference is to
employ not more than about 10 weight percent of such additives on a total
toner powder composition weight basis.
Suitable dry styrene-acrylic copolymer toners can optionally incorporate a
small quantity of low surface energy material in combination with toner
particles comprised of polyester polymer, as described in U.S. Pat. Nos.
4,517,272 and 4,758,491. Optionally the toner can contain a particulate
additive on its surface such as the particulate additive. disclosed in
U.S. Pat. No. 5,192,637.
The charge control agent and other addenda can be added to the toner in a
number of ways. For example, in a dry electrostatographic-toner, the
charge control agent can be mix-blended in the manner described in U.S.
Pat. Nos. 4,684,596 and 4,394,430, with an appropriate polymeric binder
material and any other desired addenda. The mixture is then ground to
desired particle size to form a free-flowing powder of toner particles
containing the charge agent. A preformed mechanical blend of particulate
polymer particles, charge control agent, colorants and additives can,
alternatively, be roll milled or extruded at a temperature sufficient to
melt blend the polymer or mixture of polymers to achieve a uniformly
blended composition. The resulting material, after cooling, can be ground
and classified, if desired, to achieve a desired toner powder size and
size distribution. For a polymer having a T.sub.g in the range of about
50.degree. C. to about 120.degree. C., or a T.sub.m in the range of about
65.degree. C. to about 200.degree. C., a melt blending temperature in the
range of about 90.degree. C. to about 240.degree. C. is suitable using a
roll mill or extruder. Melt blending times, that is, the exposure period
for melt blending at elevated temperature, are in the range of about 1 to
about 60 minutes. After melt blending and cooling, the composition can be
stored before being ground. Grinding can be carried out by any convenient
procedure. For example, the solid composition can be crushed and then
ground using, for example, a fluid energy or jet mill, such as described
in U.S. Pat. No. 4,089,472. Classification can be accomplished using one
or two steps.
In place of mix or melt blending, the polymer can be dissolved in a solvent
in which the charge control agent and other additives are also dissolved
or are dispersed. The resulting solution can be spray dried to produce
particulate toner powders. Limited coalescence polymer suspension
procedures as disclosed in U.S. Pat. No. 4,833,060 are particularly useful
for producing small sized, uniform toner particles.
The carrier and developer of the invention can be used in a variety of ways
to develop electrostatic charge patterns or latent images. Such
developable charge patterns can be prepared by a number of means can can
be carried, for example, on a light sensitive photoconductive element or a
non-light-sensitive dielectric surface element, such as an insulator
coated conductive sheet. One suitable development technique involves
cascading developer across the electrostatic charge pattern. Another
technique involves applying toner particles from a magnetic brush. This
technique involves the use of magnetically attractable carrier cores.
After imagewise deposition of the toner particles the image can be fixed,
for example, by heating the toner to cause it to fuse to the substrate
carrying the toner. If desired, the unfused image can be transferred to a
receiver such as a blank sheet of copy paper and then fused to form a
permanent image.
The following Examples and Comparative Examples are presented to further
illustrate some preferred modes of practice of the invention. Unless
otherwise indicated, all starting materials were commercially obtained.
Comparative Examples 1-4
Carrier was prepared by melt coating 2 parts per hundred of PVF.sub.2
(Kynar 301F) onto a strontium based hard ferrite carrier core. Developer
was prepared by mixing the carrier with a styrene/acrylic toner having a
positive charge control agent and carbon black pigment (Ektaprint K toner,
marketed by Eastman Kodak Company of Rochester, N.Y.). The developer toner
concentration was varied from 8 to 16 weight percent in Comparative
Examples 1 through 4. The charge to mass measurements were made on MECCA
device using a fully charged developer. The MECCA measurement method
involves first preparing 4.0 grams of developer by mixing the toner with
carrier particles. The mixture was gently agitated in a appropriate bottle
or vial to allow the developer to reach its optimum maximum charge. This
was achieved by a wrist-action-robot shaker operating at 2 Hz and an
overall amplitude of 11 cm, for 2 minutes. The toner charge level was
measured by placing 0.05 to 0.2 grams of charged developer in a sample
dish situated between electrode plates and subjecting it, simultaneously
for 30 seconds, to a 60 Hz magnetic field to cause developer agitation and
to an electric field of about 2000 volts/cm between the plates. Some toner
is released from the carrier surface and is attached to and collected on
the plate having polarity opposite to the toner charge. The total toner
charge was measured by an electrometer connected to the plate. The toner
charge divided by the weight of the toner on the plate yielded the charge
to mass of toner in microcoulomb per gram (.mu.Coul/gm). The aged or
exercised charge/mass results were obtained on an exercised developer by
placing 4.0 grams of developer into plastic vials, capping the vials, and
placing each vial, for 10 minutes on a "bottle brush" device comprising a
magnetic toner roller with a stationary shell and a magnetic core rotating
at 2000 rpm. The magnetic core had 12 magnetic poles arranged around its
periphery in alternating north-south fashion. The charge to mass
measurements were performed on each aged developer using the MECCA device
as described above.
TABLE I
______________________________________
Charge/Mass Results on Various Developers
based on Ektaprint K Toner and 2 pph Kynar Coated
Ferrite Carrier
Toner Fresh Fresh 10 min 10 min
Comp. conc TC Q/M BB TC BB Q/M
Ex. (wt %) (wt %) (.mu.C/g)
Devpd (.mu.C/g)
______________________________________
Comp. 8 8.2 31.3 7.3 6.7
Ex 1
Comp. 10 10.0 31.8 9.6 8.6
Ex. 2
Comp. 12 11.7 30.6 11.6 12.6
Ex. 3
Comp. 16 15.8 27.7 15.7 15.0
Ex. 4
______________________________________
These results show that the charge of the toner drops when developer is
aged without replenishment. The data show that higher toner concentration
is better for reducing the effect of unreplenished aging.
EXAMPLE 5a-5g
In this example, the mechanical deformation of the carrier was carried out
by placing the coated carrier alone for various time periods on a magnetic
brush roller in which the core was rotated at 2000 rpm. The core consisted
of alternating north-south placement of the magnets along the periphery of
the shell. The stabilized carrier was then used to prepare developer
samples at 12 percent toner concentartion using the same toner as in
Example 1-4. The charge to mass results obtained on the MECCA device are
summarized in Table II. The results shows that when the carrier had been
subjected to mechanical deformation by placing it on a magnetic roller for
various time intervals, causing a phase transformation from .alpha. to
.beta. form an improvement in the aging behavior of the developer is
realized.
TABLE II
______________________________________
Charge/Mass Results on Various Developers
based on Ektaprint K Toner and 2 pph Kynar Coated
Ferrite Carrier at 12% TC
Bottle
Brush Fresh 10 min 10 min
Exercise Fresh Q/M BB TC BB Q/M
Ex. Time TC (.mu.C/g)
Devpd (.mu.C/g)
______________________________________
Ex. 5a 0 11.7 30.6 11.6 12.6
Ex. 5b 0.5 12.4 32.3 11.8 20.6
Ex. 5c 1.0 12.5 33.6 11.8 23.7
Ex. 5d 2.0 12.5 32.4 12.2 29.6
Ex. 5e 4.0 12.4 30.3 12.2 30.7
Ex. 5f 8.0 12.3 31.2 12.3 29.4
Ex. 5g 16.0 12.3 30.0 12.1 29.4
______________________________________
COMPARATIVE EXAMPLES 5-6 AND EXAMPLES 6-7
For the purpose of controlling the charge/mass of the developer, carrier
coating were also prepared in substantially the same manner as the
previous Examples using a mixture of PVF.sub.2 and
poly(methylmethacrylate) (PMMA) at 2 pph of total coverage. The charge to
mass results for developers based on these carriers are shown in Table
III.
EXAMPLE 8
In an alternate method to provide mechanical deformation to the carrier
surface, the coated carrier was placed in a Processall device and agitated
for 4 hours. Following this mechanical agitation, the exercised carrier
was used to prepare developers in substantially the same manner as in the
previous examples and the results are presented in Table III. The
comparison between Example 7 and 8 exhibits that similar improvement can
be realized equally by both methods of stabilization. Compared to the
unstabilized carrier, the stabilization method of the invention helps in
charge stability. But the with less than 100 percent Kynar coated carrier,
the biggest improvement is found in the formation of correct signed
particles. The last example in Table III involves carrier stabilization in
Processall as opposed to magnetic brush. Similar improvement in
performance is observed with this technique of carrier stabilization.
TABLE III
______________________________________
Charge/Mass Results on Various Developers
based on Ektaprint K Toner and Various Coated Ferrite
Carrier at 10% T.C.
Fresh 10 min
10 min
C. Ex Fresh Q/M BB TC BB Q/M
and Ex. Carrier TC (.mu.C/gm)
Devpd (.mu.C/gm)
______________________________________
C. Ex. 5
1 pph 10.2 24.2 5.5 1.8
Fresh
Ex. 6 1 pph Aged
10.1 22.7 9.7 13.6
C. Ex. 6
1.5/0.5 10.4 20.5 7.3 3.0
Fresh
Ex. 7 1.5/0.5 10.1 20.0 9.4 7.5
Aged
Ex. 8 1.5/0.5 10.4 22.1 9.3 6.0
Aged
Processall
______________________________________
COMPARATIVE EXAMPLES 7-10 AND EXAMPLES 9-12
These examples and comparative examples consist of various carrier coatings
of Kynar and PMMA prepared in substantially the same manner as the
previous examples except for the substitution of blue pigment in place of
carbon. All carriers were impacted in a Processall for 4 hours to help
stabilize the charge. The charge/mass results for these carriers along
with their controls are presented in Tables IVa-IVb. All results show that
the method of the invention provides unexpected charge stability results.
Additionally, this approach is also very economical and simple.
EXAMPLE 13
The off-line machine performance of developers prepared with stabilized
carriers was carried out a LTD device. The LTD device consists of a
developer station about 4 inches long which is similar in design to the
developer station in a Kodak 1575 Copier Duplicator. It holds
approximately 250 g of developer. Developer is skived to control the
thickness of the developer nap. Toner is developed onto a rotating drum by
imposing a bias of 0 to 200 volts between the developer roller and the
drum. The drum is cleaned by a steel blade, and the used toner is conveyed
into a collection bottle. The toner concentration is controlled by a
magnetic monitor which drives a toner replenisher.
A manifold is fitted to the top of the developer station and connected to
laboratory vacuum through a filter. Dust generated in the development nip
is collected in the filter and weighed periodically. Thus, the rate of
dusting can be determined as the developer ages. This dust is referred to
below as "on-line" dust.
The toner replenishment rate is about 0.1 gram of toner per gram of
developer per hour which is similar to toner usage expected for a 1575
copier-duplicator. Therefore, each hour of testing corresponds to about
4000 copies. The charge/mass and dusting data are shown in FIGS. 1-3.
EXAMPLE 14
Developers were prepared as in Example 8, but with different stabilization
times in the Proccessal device. Results were then obtained using an
Ektaprint 2085 copier equipped with a SPD developer station (as disclosed
in U.S. Pat. No. 4,878,089, which is hereby incorporated herein by
reference. FIG. 4 shows the results of the different developers in this
machine in which the carrier had been stabilized for various time
intervals on a Processall machine. The results again confirm the developer
stability in a machine environment. The increase in the stabilization time
also help in the overall process stability as flat toner concentration and
Vzero response are obtained. This carrier conditioning approach does not
affect the overall image quality as indicated by the measurements on
linewidth ratio, 0.6 neutral density mottle, solid area mottle and
background.
TABLE IVa
______________________________________
Charge/Mass Results on Various Developers
based on Various Stabilized Carriers with Blue Toner at
10% TC
Ex. or Fresh Fresh
C. Ex. Kynar/PMMA Stabilization
TC Q/M
______________________________________
C. Ex. 7
0.6/0.9 No 8.3 3
Ex. 9 Yes 10.1 9.0
C. Ex. 8
1.3/0.7 No 10.0 10.0
Ex. 10 Yes 10.0 10.0
C. Ex. 9
1.4/0.6 No 9.4 11.0
Ex. 11 Yes 10.6 13.0
C. Ex. 10
1.5/0.5 No 9.6 13.0
Ex. 12 Yes 10.0 15.0
______________________________________
TABLE IVb
______________________________________
Charge/Mass Results on Various Developers
based on Various Stabilized Carriers with Blue Toner at
10% TC
Ex. or 10 min
C. Ex. 10 min TC Q/M 1 Hr TC 1 Hr Q/M
______________________________________
C. Ex. 7
0 0
ve
ve
Ex. 9 9.7 5.0 1.3 9.0
C. Ex. 8
9.6 4.0 1.9 5.0
Ex. 10 10.0 10.0 8.3 4.0
C. Ex. 9
9.1 6.0 3.0 5.0
Ex. 11 10.5 16.0 10.2 6.0
C. Ex. 10
9.7 11.0 7.9 2.0
Ex. 12 10.1 22.0 9.7 10.0
______________________________________
While specific embodiments of the invention have been shown and described
herein for purposes of illustration, the protection afforded by any patent
which may issue upon this application is not strictly limited to a
disclosed embodiment; but rather extends to all modifications and
arrangements which fall fairly within the scope of the claims which are
appended hereto:
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